Covered rolls are used in demanding industrial environments in which they are subjected to high dynamic loads and temperatures. Covered rolls can be used not only for transporting material under process, which is often in the form of a travelling web, but also for processing the web itself into a finished product.
A bowed roll is a specific variety of industrial roll used to correct web distortion and similar problems by distributing lateral tension evenly across a travelling web. For example, bowed rolls can be used to spread out or expand the travelling web for the purposes of maintaining width, eliminating wrinkles, eliminating baggy centers or slack edges. Bowed rolls can also be used to control felts by maintaining their width, openness and seams, and to eliminate interleaving of individual slit webs on winders.
A press roll is another type of industrial roll which is typically employed in nip presses. Press rolls process the travelling web by compressing the web at the nip between the rolls. Typically, this is done to remove liquids from the web (such as in dewatering presses), or to eliminate high and low spots in a finished product (such as in finish nip presses).
Bowed rolls and press rolls often include elastomeric sleeves or compliant elastomeric covers, particularly when they are employed in processes in which a web under process is coated with surface enhancing materials that are tacky. As a result, these materials are susceptible to transferring from the web to the surface of the roll, which can result in the degradation of the surfaces of the roll and the web. As such, it is desirable to have such rolls coated with a material that it is self-cleaning (i.e., it can release material that would otherwise tend to adhere to it).
At present, industrial rolls having release surfaces are treated with epoxies, urethanes, PTFE polymers, silicones or waxes. Epoxies and urethanes have desirable abrasion resistance properties, but typically lack the desired high release properties and low coefficients of friction. PTFE polymers and silicones have high release properties and low coefficients of friction, but generally lack high abrasion resistance qualities. Waxes and silicone polish coatings typically lack durability.